The present invention relates to an improved, spin-on high-pressure fluid filter of the type having a bead-lock arrangement in lieu of a rolled lock seam to secure the cover to the housing, wherein the improvement comprises the use of a low-cost cover assembly formed from stamped metal plates, as well as a method of assembly thereof.
Spin-on filters have been employed in a variety of applications including hydraulic systems and engine lubrication systems. Such filters generally include a filter element within a housing with a cover or nut plate secured at one end of the housing by which the filter can be screwed onto or off of a filter head. A central opening surrounded by a plurality of smaller openings is provided in the cover to direct flow through the filter element contained within the housing of the filter. In an inside/out flow arrangement, pressurized, unfiltered fluid (such as the lubricating oil used in a diesel engine) enters the central opening and exits through the surrounding openings after passing through the filter element within the housing. In an outside/in flow pattern, the pressurized, unfiltered fluid enters the surrounding-openings and-exits through the central opening after passing through the filter element. A circular gasket is provided on a top surface of the cover to serve as a seal between the filter and the filter head. A spring is provided at the lower end of the housing to push the filter element in sealing engagement with the underside of the nut plate that forms the cover.
Although satisfactory in low and medium applications, generally spin-on filters of the prior art have not been satisfactory for use in high-pressure applications such as in hydraulic transmission pumps, where surges of 1,000 psi or more can occur. Most spin-on filters currently available include covers constructed of a stamped steel disk, and a relatively thinner secondary disk spot welded thereto. The base disk includes an extruded, relatively shallow, internally threaded neck portion by which the filter can be connected to a filter head. Flow openings are punched into the base disk around the neck portion. The lip at the open end of the housing is connected, by means of a rolled lock seam, to the periphery of the secondary disk which is also formed to serve as a seat for the external gasket. In this design, fatigue failure is most likely to occur at the rolled lock seam or at the spot welds. A burst failure is most likely to occur either upon bending of the cover (which allows leakage to pass the external gasket) or upon unfolding of the rolled seam. Thus, prior art spin-on filters have been susceptible to failure at the cover and/or at the connection between the cover and housing. Welding of the housing and cover is often unacceptable due to the incompatibility of housing and cover materials such that a satisfactory weld cannot be formed.
To solve these problems, the applicants developed a novel high-strength, spin-on filter in which a reliable and durable seal between the cover and the open end of the housing was achieved without the use of either a rolled lock seam, or a weld by means of a bead-lock arrangement. This filter is described and claimed in U.S. Pat. No. 5,080,787, assigned to the Fleetguard, Inc., the entire specification of which is incorporated herein by reference. In this particular filter, a round cover formed from die-cast metal is provided which is circumscribed around its outer edge by both an upper, C-shaped groove and a lower groove having a rectangular cross section which seats an O-ring. The die-cast cover further includes a centrally located, threaded aperture which can be screwed onto the nipple of a filter head, and a plurality of oil outlet openings surrounding the threaded, centrally-located aperture. On the top surface of the die-cast cover, a circular groove is provided which circumscribes the outlet openings that surround the threaded aperture. This groove receives a gasket which creates a seal between the top surface of the cover of the filter and the filter head when the threaded aperture of the filter cover is screwed onto the threaded nipple of the filter head. In the method of assembling this prior art filter, the filter element is first placed into the interior of the housing. An O-ring is then seated around the second groove which circumscribes the lower part of the die-cast cover, and the cover is then inserted into the open end of the housing until the C-shaped groove which circumscribes the upper portion of the housing is positioned adjacent to the upper periphery of the housing. A roller is then used to inwardly deform the metal around the periphery of the housing in conformance with the C-shaped groove in the cover in what is known in the art as a xe2x80x9cspin beadingxe2x80x9d operation. The spin-beading secures-the cover to the housing without the need for rolled lock seams which, as previously pointed out, are proven to rupture when exposed to high pressures. The use of a spin-beading operation to secure the cover to the housing, instead of a lock seam, allows this filter to be assembled rapidly and inexpensively.
While the filter disclosed and claimed in U.S. Pat. No. 5,080,787 represents a substantial advance in the art, the applicants have observed two areas where improvement would be desirable. First, while the die-cast cover used in this filter works well for its intended purpose, it is unfortunately expensive as compared to covers formed from one or more stamped metal plates. Secondly, because the seal between the cover and the housing is dependent upon the proper compression of the O-ring between the cover and the housing, the dimensional tolerances of the O-ring, and the depth of the groove in the cover that seals it are narrow. These narrow tolerances prevent the substitution of a less precisely dimensioned, but lower cost lathe-cut gasket for the O-ring. Thirdly, when the cover is inserted into the open end of the housing incident to the assembly operation, shear forces are applied to the O-ring that has been previously seated around the lower circumferential groove of the cover which are capable of either damaging the O-ring, or rolling it out of the lower circumferential groove of the cover, thereby destroying the cover seal. While the application of a lubricant to the seated O-ring prior to the insertion of the cover into the housing solves much of this problem, it also adds an unwanted step in the assembly operation.
Clearly, it would be desirable if an improved filter could be developed which maintained all of the structural and assembly advantages associated with the filter disclosed and claimed in the ""787 patent, but whose cover could be replaced with a lower cost cover assembly formed from stamped metal plates and lathe-cut gaskets. It would further be desirable if the assembly of such an improved filter did not apply unwanted shear forces onto any of the sealing O-rings or gaskets during the assembly of the filter, and did not require the application of any O-ring or gasket lubricants.
It is an object of the present invention to provide a method of assembly an improved filter which maintains all of the advantages associated with the filter disclosed and claimed in U.S. Pat. No. 5,080,787, but which is less expensive and easier to manufacture.
It is a further object of the invention to provide such an improved filter which utilizes a relatively inexpensive cover assembly formed from stamped metal plates and lathe-cut gaskets, and which does not require the application of any lubrication to the sealing gaskets.
Finally, it is an object of the invention to provide an improved method of assembling a filter in which none of the O-rings or sealing gaskets is subjected to shear forces; during the assembly of the filter which could either damage or misalign the sealing gaskets.
To this end, the filter of the invention comprises a method of assembling a filter including housing having a periphery that includes an inwardly deformed portion, and a cover assembly including a cover plate and a retainer plate having mutually spaced apart outer edges for forming a recess that receives the inwardly deformed portion of the housing. A gasket is disposed in the recess defined by the mutually spaced apart outer edges for effecting a seal between the outer edge of the cover assembly and the inwardly deformed portion of the housing when said portion is inwardly deformed incident to a spin-beading operation.
In the preferred embodiment, both the cover plate means and the retainer plate are formed from a stamped metal, such as steel. Additionally, the retainer plate further includes a deformed portion located inside of its outer edge that defines a groove for receiving a second gasket for effecting a seal between the cover assembly, and a filter head. One of the walls of the deformed portion of the retainer plate may function to compress the first gasket when this gasket is engaged by the spin-beaded portion of the housing. Finally, the deformed portion of the retainer plate may have an exterior portion that acts as a spacer to uniformly space apart the outer edges of the cover plate and retainer plate.
The outer edges of the retainer plate may be dimensioned to extend over the periphery of the housing to limit the extent to which the cover assembly may be inserted into the housing during the assembly thereof. These outer edges may be deformed into frictional engagement with the inwardly deformed portion of the housing to prevent relative rotation between the cover assembly and the filter housing when the filter is screwed into a nipple of a filter head.
The invention encompasses a method of forming such a fluid filter which comprises the steps of providing a filter housing as previously described, placing a filter element within the housing, forming a cover assembly with first and second plates by interconnecting the two plates together so that they have mutually spaced apart outer edges that define a recess, seating a gasket in the recess, inserting the cover assembly into the open end of the housing such that the periphery of the filter housing is adjacent to the recess, and deforming at least some of the housing periphery inwardly into the recess to both secure and seal the cover assembly to the housing.
The method of the invention may further comprise the step of stamping a deformed portion in the first plate that is offset with respect to the outer edge of the first plate and using this offset portion to uniformly space apart the outer edges of the first and second plates to form the recess. In the preferred method of the invention, the deformed portion of the first plate defines a groove, and the method further includes the step of seating a second gasket in the groove which forms a seal between the filter and a filter head when the filter is secured onto the head.
The improved filter allows the cover assembly to be made of inexpensive stamped steel plates, and further allows the substitution of a less expensive lathe-cut gasket for the O-ring used in the prior art. The improved filter also obviates the need for applying potentially damaging shear forces to the gasket that seals the cover assembly to the housing, or lubricants to minimize the damaging effects of such forces, as the gasket does not engage the housing until the bead rolling step.